Reference may be made to U.S. Pat. Nos. 3,803,245 and 3,994,968 wherein acylation of 2-methoxynaphthalene is carried by aluminum chloride in nitrobenzene. The inherent disadvantages in the use of conventional Lewis acid metal chlorides for Friedel-Crafts acylation are that they are non-regenerable and require more than stoichiometric amounts because of strong complexation with the carbonyl product formed. Work-up to decompose the resultant intermediate complex by hydrolysis results in the generation of a large amount of waste product and employment of lengthy, cumbersome and expensive separation process. Reference may be made to U.S. Pat. Nos. 4,593,125 and 4,670,603 wherein naphthyl ethers are acylated with carboxylic acids, carboxylic acid halide or anhydrides in anhydrous hydrofluoric acid. The drawbacks are that hydrofluoric acid is extremely toxic, corrosive, and thus warrants maintenance of stringent safety conditions and requires expensive equipment in order to work with hydrofluoric acid. Further the use of hydrofluoric acid as a solvent, generates large amounts of salts as effluents upon neutralization.
Reference may be made to a publication by Prins et al., Studies in Surface Science and Catalysis, 94, 397, 1995 wherein naphthyl ether in sulfolane solvent is acylated with acetic anhydride using zeolite H.sup.30 -beta obtained through various options. The drawback is that the selectivity towards 6acetyl-2-methoxynaphthalene, a desired regiomer, is poor.
Reference may be made to a publication by Choudary et al., Applied Catalysis A; 171, 159, 1998 wherein aromatic ethers are acylated with acid anhydrides in the presence of metal ion exchanged clays with moderate to good yields. The drawback is that the selectivity towards 6-acetyl-2-methoxynaphthalene is very poor.
Reference may be made to a publication by Holderich et al., Journal of Catalysis, 185, 408, 1999 wherein H.sup.30 -beta zeolite with varying acidic sites obtained through acid treatment was used to effect acylation of naphthyl ether with acetic anhydride in sulfolane solvent. The drawbacks are the yields and selectivities are moderate.
Reference may be made to a U.S. Pat. No. 5,277,529 wherein the acylation of naphthyl ethers with carboxylic acids, anhydrides or chlorides was carried out both in liquid phase and vapour phase employing H.sup.30 beta zeolite. The drawback is that the yields are poor (9-35%).